The present invention is directed toward an improved process for the dehydrogenation of dehydrogenatable hydrocarbons. More particularly, the described inventive technique is an improved means of providing heat of reaction to a catalytic dehydrogenation reaction zone, reducing the magnitude of the temperature drop in the reaction zone and providing a higher per pass conversion of dehydrogenatable hydrocarbons to their corresponding olefins.
Dehydrogenating hydrocarbons is an important commercial hydrocarbon conversion process because of the great demand for dehydrogenated hydrocarbons for the manufacture of various chemical products such as detergents, high octane motor fuels, pharmaceutical products, plastics, synthetic rubbers, and other products well known to those skilled in the art.
In a typical hydrocarbon dehydrogenation process, the feed hydrocarbons are admixed with hydrogen and the resulting admixture is heated by indirect heat exchange with the dehydrogenation reaction zone effluent. After being heated in the feed-effluent heat exchanger, the feed stream is further heated by passage through a heater which is typically a fired heater or furnace. The admixture, typically referred to as the combined feed, is then contacted with a bed of dehydrogenation catalyst, which may exist as a fixed bed, a fluidized bed, or a movable bed via gravity flow. The resulting dehydrogenation zone effluent is withdrawn from the reaction zone and, after indirect heat exchange with the combined feed, it is passed to product separation facilities. Generally, the product separation facilities are employed to produce a gas stream, comprising substantially hydrogen, a portion of which may be recycled back to the catalytic reaction zone to provide hydrogen for admixture with the hydrogenatable hydrocarbon feed stream. Generally, a first product stream is produced comprising the desired product olefins and a second product stream comprising light hydrocarbons, typically known as light hydrocarbon by-products, having fewer carbon atoms per molecule than the desired product olefin. Both of these product streams may be recovered in the product separation facilities. In addition, a recycle stream comprising unconverted dehydrogenatable feed hydrocarbons may be withdrawn from the product separation facilities and recycled back into the combined feed stream. Fundamental to the catalytic dehydrogenation process is the fact that the dehydrogenation reaction is highly endothermic which results, as the reaction proceeds, in cooling the reactants to temperatures at which the dehydrogenation reaction will not proceed at any appreciable rate. To counteract this problem, additional heat must be supplied to the bed of dehydrogenation catalyst to assure reaction rates sufficient to make a commercial process economically feasible. Accordingly, many methods of supplying this additional heat have been contrived in order to make catalytic dehydrogenation a viable commercial process.